Poly (D-3-hydroxybutyrate) (PHB) is a natural biodegradable and biocompatible polyester that can be synthesized by many microorganisms and accumulated therein as carbon and energy reserve. Because PHB can be completely degraded by many microorganisms in the environment without forming any toxic products, it can be used to make biodegradable plastics (Shimao 2001). Several studies have described the isolation and characterization of aerobic and anaerobic microorganisms that can degrade PHB. Most of these studies were carried out at ambient temperatures (25° C.-30° C.) but little data is available on the microbial degradation of PHB at a higher range of temperature.
However, thermophilic composting is one of the most promising technologies in recycling biodegradable plastics, and thermophilic/thermotolerant microorganisms play an important role in the composting process. Most studies on high-temperature polyester degradation were focused on bacteria and fungi (Takeda et al., 1998; Tansengco & Tokiwa, 1998; Sanchez et al., 2000). There is still a need for thermophilic/thermotolerant microorganisms that are able to degrade polyesters under high temperature conditions.
Actinomycetes are antibiotic-producing microorganisms. There is a vast amount of reports on actinomycetes enzyme-production and degradation abilities in vitro. Actinomycetes are usually considered to be the most active microorganism in the later stages of decomposition of plant and other materials, and play an important role in polyester degradation. Some thermophilic/thermotolerant actinomycetes that can degrade polyesters have been reported. Kleeberg et al. (1998) disclose the degradation of terephthalic acid (BTA) by Thermobifida fusca (former name: Thermomonosproa fusca). Jarerat & Tokiwa (2001) disclose the degradation of poly(tetramethylene succinate) (PTMS) by Microbispora rosea subsp. aerata IFO 14046, Microbispora rosea subsp. aerata IFO 14047, Actinomadura sp. (former name: Excellospora japonica) IFO 14486, and A. viridilutea (former name: E. viridilutea) JCM 339. M. rosea subsp. aerata IFO 14046 also could degrade poly(ε-caprolactone)(PCL), PHB and poly(lactide)(PLA). Calabia & Tokiwa (2004) disclose the degradation of PHB, poly(ethylene succinate) (PES), poly(ester cargonate) (PEC), PCL, and poly(butylenes succinate) (PBS) by Streptomyces sp. strain MG. However, no thermophilic/thermotolerant PHB degradation in genus Actinomadura has been reported. We surprisingly found that a thermotolerant Actinomadura strain isolated from the environment has polyester degrading ability at a high temperature environment.